I'd stay away from maple. It really tends to twist up badly. It also is the most MISERABLE wood to try to tool. It's so hard. I used it a bit for a project and regretted it as soon as I had to start chiseling. The only thing I would use maple for is braces. Oak works very easily for a hardwood, I would recommend that.
As far as pine vs hemlock...
Hemlock gets really tough to work when it dries. It's not bad when green though. IF you have good material. Hemlock is good when it's good garbage when it's bad. I'd take pine over hemlock.
Whatever species you use, try to get winter cut wood. In my experience it makes a big difference in checking and stability.